1. Field of the Invention
This invention relates to an improvement in vehicle air bag or cushion restraint systems, and is useful, particularly in very cold weather, in air bag inflators that are provided for the passenger side of an automobile.
2. Description of the Prior Art
Safety air bag inflators or gas generators that utilize the combustion of a solid gas generant composition for the rapid generation of clean nitrogen gas for inflating air bags are known in the prior art. One efficacious form of such inflator is disclosed in U.S. Pat. No. 4,296,084 issued on Oct. 20, 1981 on the copending application Ser. No. 88,992, filed Oct. 29, 1979 by Gary V. Adams et al wherein a separate embodiment of the invention is disclosed for each of the driver and passenger sides of an automobile or other vehicle.
The inflator for the passenger side, as disclosed in U.S. Pat. No. 4,296,084, includes an elongated tubular housing with a plurality of perforations in it for discharging gas. Within the tube are filtering screens, a gas generant and an igniter. The perforations in the tube are normally sealed with thin non-tempered, 0.003 inch (0.0762 mm.) thick, aluminum foil, which is easily ruptured by gas pressure when the inflator is ignited. This foil serves as a hermetic seal for protecting the gas generant and igniter from moisture and dust. The foil also insures that the gas pressure, in its rise to a peak value upon combustion of the gas generant, will reach a certain, threshold value before being discharged into an air bag. It has been found that, in very cold weather, this inflator attains its peak pressure considerably more slowly than in warm weather so that there is a tendency for the air bag to be inflated either too slowly or insufficiently to perform its intended purpose, with consequent discomfort or possible injury to the passenger in the vehicle who is relying upon inflation of the air bag for protection.
It is known in the art to provide multi-level gas generators or inflators for inflating the air bag with the utmost rapidity if the shock of an impact is severe and less rapidly if the shock is less severe. Such an arrangement is disclosed in U.S. Pat. No. 3,972,545 granted on Aug. 3, 1976 wherein a hermetically sealed container is divided into two parts each of which contains a gas generant material and a squib. When the shock is severe a sensing means fires both squibs simultaneously. A less severe shock causes only one of the squibs to fire. There is no provision in U.S. Pat. No. 3,972,545, however, for adjusting the response of the inflator in accordance with the ambient temperature, and specifically, for increasing the response of the inflator in very cold weather.